Improving an American Elm Base

Hi all,

1st time posting here. I have what I believe to be an American Elm that I’ve been developing for a few years. I am looking to improve the nebari, in particular on the left and back side. What would be the best method of improving this - airlayer or approach & thread grafting?

It was last repotted in Dec 2020 onto a wooden board in a lava/pumice/scoria 1-1-1 mix with some root work done at that time to try to improve the roots.

I know elm are difficult with nebari due to circling roots. I also know that elm are particularly vigorous and can be difficult to air layer as the callus can grow over the layer site. But I was also advised by Ted Matson (curator of the Huntington Library’s collection) that they can be difficult to graft due to the vigorous growth.

Back to the original question - how to improve the base? If air layering, would this be a good species to leave the air layer site uncovered for a few days, similar to trident maples and and the discussion in the flowering apple stream? Could this have resonable success with root grafting (50% success or greater)?

Any ideas?